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Over the last decades, remote observation tools and models have been developed to improve the forecasting of ash‐rich volcanic plumes. One challenge in these forecasts is knowing the properties at the vent, including the mass eruption rate and grain size distribution (GSD). Volcanic lightning is a common feature of explosive eruptions with high mass eruption rates of fine particles. The GSD is expected to play a major role in generating lightning in the gas thrust region via triboelectrification. Here, we experimentally investigate the electrical discharges of volcanic ash as a function of varying GSD. We employ two natural materials, a phonolitic pumice and a tholeiitic basalt (TB), and one synthetic material (soda‐lime glass beads [GB]). For each of the three materials, coarse and fine grain size fractions with known GSDs are mixed, and the particle mixture is subjected to rapid decompression. The experiments are observed using a high‐speed camera to track particle‐gas dispersion dynamics during the experiments. A Faraday cage is used to count the number and measure the magnitude of electrical discharge events. Although quite different in chemical composition, TB and GB show similar vent dynamics and lightning properties. The phonolitic pumice displays significantly different ejection dynamics and a significant reduction in lightning generation. We conclude that particle‐gas coupling during an eruption, which in turn depends on the GSD and bulk density, plays a major role in defining the generation of lightning. The presence of fines, a broad GSD, and dense particles all promote lightning.

<p>The emergence of the first organic molecules as a fundamental step in the prebiotic assembly of life remains enigmatic. Lightning has been considered as a potential energy source for the synthesis for first organic molecules. The iconic abiotic synthesis experiments: the discharge experiments performed in 1953 by Miller and Urey [1] under simulated reducing atmosphere conditions were conducted in the absence of any geomaterial substrate. Further, new views about the composition of the Early Earth’s atmosphere have been developed which require a revisiting of the Miller experiment.</p><p>Volcanic lightning associated with volcanism provides a possible energy source, a variety of different volcanic gases and possible catalysts to synthesize a variety of primitive organic molecules. Volcanic ash particles are known for their porosity, high surface area and significant surface reactivity. Volcanic plumes themselves provide a high variety of volcanic gases including, but not limited to reducing ones, and therefore may enlarge the spectrum for possibly available gas compositions in the Early Earth atmosphere.</p><p>Recent laboratory studies have successfully recreated near-vent volcanic lightning under laboratory conditions [2,3]. We will present first insights from volcanic discharge experiments under different atmospheric compositions, varying in CO<sub>2</sub>, and N<sub>2</sub> composition to mimic some first Early Earth conditions. Special focus is given to the role of ash particles as a catalyst and container as well as the influence of gas composition on the yield of organic compounds.</p><p> </p><p>[1] Miller, S.L. (1953). A production of amino acids under possible primitive earth conditions. Science, 117, 528-529.  </p><p>[2] Cimarelli, C., Alatorre-Ibargüengoitia, M.A., Kueppers, U., Scheu, B. and Dingwell, D.B. (2014). Experimental generation of volcanic lightening. Geology, 42, 79-82.</p><p>[3] Gaudin, D. and Cimarelli, C. (2019). The electrification of volcanic jets and controlling parameters: A laboratory study. EPSL, 513, 69-80.</p><p> </p>

<p>Far from being a recent development of the Earth System, volcanism has accompanied the Earth, terrestrial planets and countless exoplanets since their origins. Volcanism is a material mechanism whereby planets evolve to their differentiated states that are potentially capable of hosting life. Explosive volcanic eruptions are commonly accompanied by volcanic lightning, modulated by charging and discharging mechanisms within the eruption column. As discharges have been proposed as a potential prebiotic synthesis mechanism for forming first organic molecules, the behaviour of volcanic lightning at early Earth conditions could yield further insights into likely environments for the origin of life.</p> <p>Earth´s atmosphere has changed significantly in composition and pressure since its early beginnings. Here, we would like to investigate how volcanic lightning might have operated and was influenced by changes in those environmental conditions. For this purpose, we have developed an experimental device, which consists of a gas-tight modification of a shock-tube apparatus, to investigate experimental discharges in decompressed jets of gas and volcanic ash particles under varying atmospheric conditions. The setup acts as a Faraday cage, capable of measuring discharges close to the vent. The gas inside the particle collector tank is sampled by crimp cap bottles and analysed by gas chromatography. We modified the enveloping atmospheric composition and pressure (200 mbar – 4 bar) and the transporting gas phase (argon and nitrogen).</p> <p>We have tested atmospheres containing carbon dioxide, nitrogen and carbon monoxide to mimic early Earth conditions and obtained discharges with similar magnitude to those achieved in an air atmosphere. We have also varied the atmospheric pressure and observed that decreasing the atmospheric pressure results in less discharges. The results of the experiments demonstrate that it is the coupling between gas and ash particles which largely governs the occurrence and magnitude of discharges close to the jet nozzle. Nitrogen as transporting gas results in fewer discharges compared to argon, emphasizing the importance of the composition of the transporting gas phase in the jet charging and discharging mechanisms. The preliminary results point to active volcanic settings under varying atmospheric conditions as multivariate environment for the emergence of life and thus our experiments continue.  </p>

Self‐ignition during the explosive eruption of mud volcanoes can create flames that in some cases reach heights that exceed hundreds of meters. To study the controls on electrical discharge in natural mud, we performed laboratory experiments using a shock‐tube apparatus to simulate explosive eruptions of mud. We vary the water content of the mud and proportions of fine particles. We measure electric discharge within a Faraday cage and we use a high‐speed video camera to image the eruption of mud and some of the electric discharge events. We find that (a) decreasing the proportion of fine particles and (b) increasing water content each suppress the number and magnitude of electric discharge events. Experimentally observed mud volcano lightning occurs where particles exit from the vent and within the jet of erupting particles.